Synchronism correction for telegraph systems



I Aug. 20; 194Q R. E. MATHES SYNCQRONISM CORRECTION FOR TELEGRAPHSYSTEMS 2 Shets-Sheet 1 m 00am Q Filed Oct. 16, 1937 INVEN TOR. R/ HARDE. MATHES BY 7%? ATTORNEY.

Aug. 20, 1940.

E. MATHES SYNCHRONISM CORRECTION FOR TELEGRAPH SYSTEMS 2 Sheets-Sheet 2DASH SPACE Will;

i I I l I I t'k zcr/ 4 z m -1..- m e f F a M m w II II 6 v W m 5 m W VIrI IIII M m w 6 F 2 Q. P. m F 6 I'm 4 LP 4 INVENTOR.

WW L ZEK Fufuufun INCOM/NE TELEGRAPH RICHARD E. MATHES.

Patented Aug. 20, 1940 UNITED STATES PATENT OFFICE SYNCHRONISMCORRECTION FOR TELEGRAPH. SYSTEMS Richard E. Mathes, Westfield, N. J.,assignor to Radio Corporation of America, a corporation of DelawareApplication October 16, 1937, Serial No. 169,365

10 Claims.

mining the need for correction from the phase 15 relationship existingbetween these steep wave fronts and the time of. occurrence of a localcircuit closure. Circuits of this known type are described in my UnitedI States Patents Nos. 2,038,375 and 2,062,009; granted April 21, 1936,

20 and November 24, 1936, respectively. These known systems, however,are unsatisfactory when there exists large bias distortion on thetelegraph circuit.

The present invention is' designed to overcome time of occurrence of alocal circuit closure, and

the end of the signal element and the time of occurrence of anotherlocal circuit closure. The times of occurrence: of these two localcircuit 35 closures are so arranged that they occur either at I the sametime coinciding with the center of a signal of one unit length (i. e.,the dot or baud),

or at different times equally disposed on both.

sides of the center of a signal of one unit length.

A better understandingof the invention may be had by referring to'theaccompanying drawings, wherein Fig. 1 discloses a circuit arrangement atthe receiver of a telegraph system for accomplishing correction inaccordance with the present invention when audio frequency tone signalsare received over the line; Fig. 2 illustrates graphically the receivedtone message signals, and the voltages on the condensers Cl, C2 atvarious times during the signal, as they are available for correctionpurposes; and'Fig. 3 is a modification of the system of Fig. 1 adaptedfor the reception of direct current telegraph signals on the line.

Referring to Fig. 1 in more detail, there is 55 shown a motor 20 fordriving the multiplex equipment of the telegraphreceiver, which motor itis desired to accurately synchronize with regard to a motor at a distanttransmitting station. Motor 20 is under control of a small correctionmotor 2|, in turn responsive to the operation 5 of a differentialelectromagnetic relay 22 across Whose winding are a pair ofdifferentially operating vacuum tubes 23 and 24.

The incoming message waves which are in the form of audio frequencykeyed tone signals arrive over line I and are rectified in full Waverectifiers' 2 and 3 for providing across the condensers 4 and 5 suitablevoltages which are applied to the grids 6 and I of the vacuum tubes 23and 24.

A pair of kicker commutators 8 and 9, together with associated apparatus(to be described later), serve to control thedischarge of the voltagesstored on condensers 4 and-5. These commu-i tators 8 and 9 each comprisea rotating insulated device across whose length is a suitable metal bar.III for short-circuiting a pair of brushes ll,

l2, or l3, l4. Each of the kicker commutators 8 and 9 are driven bysuitable shafts l5, in turn linked to the drive motor 20, as shown bythe dotted lines I6 and I1. Amore amplified description of thesecommutators is given in my United States Patent No. 1,963,587, grantedJune 19, 1934. These kicker commutators may, of course, be of anysuitable form to provide a circuit clo-' sure.

The audio frequency keyed tone signal received over transmission line Iis' fed to rectifiers 2 and 3 over audio frequency transformers l8 andI9, respectively. Upon receipt of the first signal element, whether itbe a dot or a dash, the recti- 5 fied tone signal produced by rectifier3 will produce a potential drop through resistance 32, thus biasing thefirst grids of vacuum tubes 23 and 24 negatively, causing these tubes tocease passing current. It will thus be seen that during the 40 actualreception of the message waves, tubes 23 and 24 will be inoperative toeffect the operation of relay 22. Vacuum tubes 23 and24 are effective,however, only during the space between signal' elements when no currentis being rectified. 5 With the functioning of rectifier 3, the receivedwaves will cause'a sudden rush of current to be applied to the primaryof audio frequency transformer 25, which will, in turn, generate in itssecondary a sharp voltage pulse of a proper polarity to cause the gridof a gaseous conduction device 26 to become positive. Device 26 is ofthe well known Thyratron'type which passes current in its anode circuitwhen a positive pulse of suitable value is applied to its grid. Thissharp pulse 56 25 the commutator 9-which shortcircuits the anode oncondenser 21 is produced when glow tube 26 I, strikes, by the passage ofcurrent through the bias battery 29 and grid resistor 4|, and thischarge is of proper polarity to overcome the bias on the grid of tube 28produced by the battery 29, thus enabling tube 28 to pass currentmomentarily. Since this .pulse across condenser 21 is only momentary,the tube 28 will cease to pass current almost immediately after thedischarge of condenser 5, subsequent to which condenser 5 will chargedue to the passage of current in the anode circuit of Thyratron 26. Theanode circuit of the Thyratron 26 includes relatively high resistances30 and 3! arranged in series, the latter of which isconnected acrosscondenser 5. Condenser 5' will continue to charge due to the. passage ofcurrent in the Thyratron 26, until such time as the glow in tube 26 isextinguished by circuit of'tube 26 through brushes l3 and I4.

- Condenser 5 will retain its charge,'except for the comparatively 'slowleakage through high resistance 3 I, at the value dependent upon theinterval between the cessation ofcurrentinvacuum tube 28 and the closureof brushes l3 and I4. Since for practical purposes the vacuum tube 28passes current only momentarily at the start or the signal element, itcan be'said that condenser 5 is charged inthe interval between the startof the signal and the closure of brushes I3 and I4. The

charge on condenser 5 will be retained until such time as gaseousconduction device 26 functions to cause tube 28 to again operate. Thischarge on condenser 5 is utilized to affect vacuum tube 24 through itsgrid 1, which is directly con, nected to one plate of the condenser5,-as shown.

At this time, it should be noted that commutators 8 and '9areeacharranged to close their respective brushes once during eachsignal element of dot length, it being understood, of course,

that in the Continental Morse Code the dash is equal to'three dots. Forthe purpose of this description, it will be assumed that kickercommutators 8 and 8 both close their respective brushes at the same timeand that this time coincides with the center of the dot. Where a dash.

is being received, there will thus be three closures for each of thekicker commutators during-a dash,-

since each dash has af length equal to three dots.

Simultaneously with the'functioning of rectifier 3, the receivedwaveswill appear across rectifier 2 and cause a sudden rush of chargingcurrent to be applied to condenser 4 through resistor 40. Due to thispulse produced at the start of the signal element, condenser 4 willslowly charge until such time as the kicker commutator 8 closes andshorts itsbrushes H and I2. When this occurs, a pulse through secondarywinding 33 of the transformer l8 will cause the application of aposition potential to the grid of a gaseous conduction-device 34, alsoof the Thyratron type, in turn producing a discharge of the condenser 4.The glow in Thyratron 34 will be extinguished immediately upon thedischarge of condenser 4, due to the action of the discharge, whichreduces the voltage on condenser 4 to a value not greater than theextinction voltage of the Thyratron tube. Condenser 4 will again startcharging immediately after its discharge,

and this charging will continue until the end of the signal element, atwhich time condenser 4 will maintain the charge it then has. For signalslonger than one unit length (length of one dot) condenser 4 will bedischarged once for each unit length due to the fact that commutator8will cause the Thyratron 4 to strike each time brushes II and I2 of thecommutator are shorted while signals are received. It willthus be seenthat the final charge on condenser 4 for each signalis a function of thetime between the-closure of.

brushes II and I 2 on the commutator 8 and the end of the signalelement.

In reviewing what has been said above, it will I be observed that thecharge on condenser 4 which is available for aifecting grid 6 of vacuumtube 23,

'is the function of the time between the last circuit closure of kickercommutator 8 and the end of the signal element, whereas the charge oncondenser which is available for aifecting the grid 1 of the vacuum tube24 is the function of the time between the start of the signal elementand the first subsequent circuit closure of kicker commutator 9. Ifthese two time intervals are equal, then synchronism between thetransmitting-rotating mechanism and motor of the receiving mechanism iscorrect. If, however, the time intervals are unequal, there is aninequality in the charges of condensers 4 and 5 which provides means forcorrecting for the departure from synchronism of the receiving motor 20.This correction is achieved as follows:

- During the spacing or no-signal interval, there no current flow or IRdrop in resistance 32,

for which reason the first grids of tubes 23 and 24 assume the bias oftheir respective cathodes. During this interval of no-signal current,tubes 23 and 24 will pass current, depending upon the voltages on grids6 and I which are produced by the respective charges of condensers 4 and5.

I Any difierences in the charges on condensers 4 and 5 will thusmanifest themselves on the grid circuits 6 and 1 of the vacuum tubes 23and 24, causing the operation of polar relay 22 in one sense or theother depending upon which tube has the greater voltage applied, to itscontrol grid, to make the correction motor 2| run in one direction orthe other, thereby to rotate the field of the motor 28. The correctionmotor'will thus I function, depending upon whether a positive or anegative current is passed thereto by the engagement of the armature ofrelay 22 with eitherits upper or its lower contact. Resistances 35 and36 and condensers3land 38 function as filters to smooth the .fiow ofcurrent through the relay 22, and to integrate it over several units ofsignal length in order to reduce hunting and minimize the effect of anyfortuitous distortion on the signal.

The operation of the system may perhaps be better comprehended byreferring to Fig. 2 which illustrates, by way of example only, thecharges on the condensers 5 and 4 during the receipt of a signalconsisting of a dash, a space, a dot, a space, and another dash. For thepurpose of this figure, it is assumed that the kicker commutators 8 and9 both operate simultaneously. The first dash extends from A to D, whilethe second dash extends from G to J. The dot extends from letters is thetime interval of one dot or one unit of signal length. The verticallines indicate the I during the-spacing interval between the dashesandthe dot, there is a blank space between them. Curve 2 indicates theenvelope of the rectified tone signal after it has passed through eitherrectifier 2 or 3. Curve 3 illustrates the building up and the dischargeof the voltage across condenser 5. It should be noted that the currentin condenser starts to build up a very short time after the start of thesignal pulse. This is because for an extremely short interval after thestart of the signal, the charge on this condenser is brought to zero bythe action of tube 28 which is only momentarily conductive. The voltageon condenser 5 builds .up until the closure of the kicker commutator 9,which occurs at a time coinciding with the mid-point of each signalhaving a duration of at least one unit length. This mid-point isrepresented by the first vertical dotted line. 'Ihe voltage on condenser5, it will be noted, is retained until the next signal element isreceived which is at E, whereupon the condenser is discharged due to thereoperation of vacuum tube 28, subsequent to which the cycle ofoperations is again repeated. Curve 4 shows that the voltage acrosscondenser 4 first builds up after the initiation of the signals untilkicker 8 operates to cause-Thyratron 34 to discharge condenser 4,whereupon condenser 4 will again build up until the next time kickercommutator 8 functions to operate Thyratron 34. Where the signal is adash, it will be observed that the voltage stored on condenser 4 isgreater in the interval between the operations of Thyratron 34 than thevoltage stored in the interval between the initiation of the signalelement and the first operation of the kicker commutator 8 A comparisonof curves 3 and 4 shows that the voltages across condensers 4 and 5, asavailable for the operation of relays 23 and 24 during the spacinginterval, are steady in value. These voltages across the condensers 4and 5 are applied to 3 tubes 22 and 23 during the spacing ornoreceived-current interval and determine the sense of operation ofrelay 22, in turn controlling the correction motor 2|. These voltagesshould be equal when synchronism is achieved, or where there is a slightdifierence in voltage on these condensers due to various circuitconstants, the difierence can be counterbalanced in the structure of thevacuum tubes 23 and 24.

An important characteristic of the operation of the present invention isthat the two kicker commutators 8 and 9 must operate once for eachsignal element of unit length, (i. e., dot or baud), or where a multipleunit signal element is received, such as the dash,they must operate oncefor every length of signal element corresponding to a unit length; inother words, three times for the dash, since the dash has a lengthequivalent to three dots. Although ,.it has been assumed above for thepurpose of exposition that the kicker commutators 8 and 9 closesimultaneously at a time coinciding with the center of the signal unit,it will be evident that commutators 8 and relays 2' the glow of tube 34to strike.

to minimize tone ripples in 9 may close at different times which areequally disposed in each signal element of unit lengthon opposite sidesof the center of the signal duration of unit length. The greater theinterval between the closures of commutators 8 and 9, the more sensitivethe system will be to variations from true synchronism and the morereadily will it correct for changes in the bias distortion. The presentinvention enables much wider changes in bias distortion than known typesof synchronization systems and also enables adjusting the point ofsynchronization to the midpoint of the signal unit (dot), whether thebias on the telegraph circuit be' heavy or light.

Fig. 3 shows a system which is substantially identical with that of Fig.1, except that the system has been modified to function with directcurrent telegraph signals on the incoming line. In this figure, therectifiers 2 and 3 of Fig. 1 have been replaced by suitableelectromagnetic and 3'. The audio frequency transformers l8 and I9 ofFig. 1 have also been omitted from Fig; 3. It will be noted that duringactual signal reception there will be a negative charge applied to theinner grids on tubes 23 and 24 by relay 3 in order to cause them tocease passing current. The receipt of signals by relays 2' and 3' willcause the respective armatures of these relays to engage their uppercontacts. During .no signal or space the armature of these relays willengage their respective lower contacts. The operation of Thyratron tube34 is here slightly different from that of Fig. 1 in that the receipt ofsignals will .causecurrentto flow. through resistor 49, here shownconnected to the lower plate of condenser 4. The ground poten-. tial ishere shown as' being positive with respect to the potential applied tothe upper contact of relay 2'. This ground potential is applied directlyto the anode of tube 34 and to the upper plate of condenser 4. When theshort circuiting bar ill of commutator 8 shorts brushes H and I2 duringthe actual receipt of signals, the grid of Thyratron 34 will be at apositive potential relative to the cathode of this tube, thus causingHowever, when no signals are being received, the armature of relay 2will be connected -to its lower contact (which is dead) and no currentwill be flowing through resistor 40. If at this time, the bar l9 shortsbrushes l1, l2, as will happen during the spacing intervals, there willbe no voltage applied to the grid oftube 34 of sufficient value to causethe glow in the tube to. strike. Battery-42 is merely a bias source forthe grid of the Thyra tron. Except for' the above mentioned difierences,the operation of the system of Fig. 3 is the same as that outlined abovein connection with Fig. 1, for which reason it is not deemed necessaryto repeat same. It will be apparent to anyone skilled in the art thatthe operation of applicantsinvention may be improved, and its efliciencyincreased by a judicious selection of bias potentials in any or all ofthe various grid circuits of the tubes, and by using common anode supplyconnections, bias voltage sources, etc. Where desired, of course,various low pass filters may be employed the output circuits of therectifiers of Fig. .1.

What is claimed is:

1. In a telegraph communication system, the

method of maintaining synchronism between disgular wave signal impulsesfrom one of saidstations, receiving said signal impulses at the otherstation, producing an electric charge Whose value is substantially afunction of the time between the steep wave front of the received signalimpulse and the occurrence of a periodic local circuit closure,producing another electric charge whose value is substantially afunction of the time between the steep wave terminus of the signalimpulse and the time of occurrence of another periodic local circuitclosure, maintaining a fi,xed

time relation between the two said circuit 'clo-' other station,producing an electric charge whosevalue is substantially a. function ofthe time between the steep wave front of the received signal impulse andthe occurrence of a periodic local circuit closure, producing anotherelectric charge whose value is substantially a function of the timebetween the steep wave terminus of the signal impulse and the time ofoccurrence of another periodic local circuit closure, causing the twosaid local circuit closures to occur simultaneously, once for everylength of signal element corresponding to a unit length 'and at a timecoinciding with the center of said unit length, and utilizing thedifference between the values of said two electric charges to correctfor departures from true synchronism.

3. In a telegraph communication system, the method of maintainingsynchronism between distributing mechanisms at two different stationswhich includes transmitting substantially rectangular wave signalimpulses from one of said stations, receiving said signal impulses atthe other station, producing an electric charge whose 'value issubstantially a function of the time between the steep wave front of thereceived signal impulse and the occurrence of a periodic local circuitclosure, producing another electric charge Whose value is substantiallya function of the time between the steep wave terminus of the signalimpulse and the time of occurrence of another periodic local circuitclosure, causing said local circuit closures to occur at different timesequally disposed on both sides of the center of every length of signalelement corresponding to a unit length, and utilizing the differencebetween the values of said two electric charges to correct fordepartures from true synchronism.

4. In a telegraph communication system, the method of maintainingsynchronism between distributing mechanisms at twodifferent stationswhich includes transmitting keyed signals at one station, translatingsaid keyed signals to audio frequency keyed tone signals, rectifyingsaid tone signals at the other station thereby to I producesubstantially rectangular wave signals,

producing from the steep wave front of said rec, tified keyed signals anelectric charge whose value is substantially a function of the timebetween the arrival of said steep wave front and the occurrence of aperiodic local circuit closure, producing from saidrectified keyedsignals another electric charge whose value is substantive peak of saidwave,

.tially a function of the time between the time of occurrence'oi'another periodic'local circuit closure and the arrival of the steep waveterminus of said signal impulse and utilizing the difference between thevalues of said two electric charges to subsequently correct fordepartures from true synchronism, said correction being applied onlyduring spacing intervals between said signals.

5. In a telegraph communication system, a receiving station having, incombination, rotating mechanism and a correction motor therefor, a

vacuum tube relay for controlling said motor, a pair of condensers forcontrolling the operation of said vacuum tube relay in opposite senses,means for charging one of said condensers only during a time intervalstarting with the arrival of the steep slope of a substantiallyrectangular Wave and ending at the norm'al ce'nterof a posimeans forcharging the other of said condensers only during a time intervalstarting with said normal center of a positive peak andending with thesteep slope termi- I nus thereof, means responsive to the dominating one'of the condenser relay in the propersense and means operative onlyduring negative peaks of said wave for enabling said relay to controlsaid motor.

6 In a telegraph communication system, a remechanism and a correctionmotor therefor, an electromagnetic three-position relay for controllinsaid motor, a pair of differentially connected vacuum tubes coupled toopposite terminals of the winding of said relay,said, tubes eachincluding a control electrode, a condenser directly connected to each ofsaid control electrodes, meansv including a gaseous conduction deviceand-a pe-' riodically operable local circuit closure for producing anelectric charge on one of said condensers whose value is substantiallyafunction ofthe time between the arrival of the steep wave front ofareceived signal impulse and the occurrence of said local circuitclosure, other means including another gaseous conduction device andanother periodic local circuit closure for producing an electric chargeon the other one. 01' said condensers whose value is substantially afunction of the time between the occurrence of the last said localcircuit closure and the occurrence of the steep wave terminus of saidsignal impulse, and a circuit responsive to the received signal impulsefor preventing the passage of cur-v rent through said vacuum tubesduring the actual reception of said signal impulse.

, rate with the rotational speed of said distributor,

means for translating each incoming intelligence signal into a singlesubstantially rectangular wave wherein the marking element'is defined bysteep front and back edges, electrostatic storage means operative tomeasure and compare two time intervals one of which is initiated at themoment of reception'of the steep front edge of a marking element and isterminated by the next succeeding one of said circuit closures, theother time interval being initiated by'on'e such circuit closure andbeing terminated by the next ensuing back edge of said marking element,and means operative'in responseto inequalities between said two timeintervals for applying phase correction to said distributor.

charges for actuating said ceiving station having, in combination,rotating 8. A system in accordance with claim 7 in which saidelectrostatic storage means comprise two capacitors, each provided withmeans for retaining its charge during the period of reception of aspacing signal. l

9. A system for correcting the phase of a receiving telegraphdistributor, comprisingmeans under control of said distributor forproducing circuit closures having a periodicity which is determined bythe cyclic operation-of said distributor, means for translating anincoming signaling wave into rectified marking and spacing signals, agaseous discharge tube having a capacitor in shunt therewith and beingprovided with means including its control grid for igniting the samemomentarily in response to one of said circuit closures which occursduring reception of a-marking impulse, thereby to discharge saidcapacitor, means operative after extinction of said tube and until thecessation of a marking signal for accumulating a charge on saidcapacitor, a second gaseous discharge tube having means connectedthereto for igniting the same at the initiation of a marking signal,means for extinguishing this tube in response to the next ensuing one ofsaid circuit closures, a second capacitor having means connected theretoand operative only during the ignition periodoi the second said gaseousdischarge tube for accumulating a charge thereon, means for retainingthe respective charges on both said capacitors during the period ofreception of an ensuing spacing signal, a three-position relay operablein accordance with the predominance of one capacitor charge over that ofthe other and efiective only during the reception of a spacing signal,and a distributor phase corrector operable under control of said relay.

10. The method'of maintaining a distributor in synchronous phase withthe arrival moments of the mean centers of a train of marking impulsesreceived over a circuit, which comprises accumulating an electric chargethe initiation of which occurs on arrival of the front edge of eachmarking impulse, causing said charge to accumulate until a predeterminedphase of the distributor cycle is reached, accumulating another electriccharge during a period which starts when another predetermined phase ofthe distributor cycle is reached and which terminates upon arrival ofthe back edge of each marking impulse, storing said charges until thearrival of a spacing impulse, then comparing the voltages of saidcharges, and accelerating orretarding said distributor in accordancewith said comparison.

RICHARD E.

